This invention relates to a thermosetting resin composition suitable for use as a molding material.
Hitherto, polyimide resin, silicone resin and the like are known as resins excellent in heat resistance. However, all these resins are limited in use for reasons that they are all expensive. Polyimide resin has a high fusion temperature and is difficult to mold, and silicone resin has a high permeability to water vapor and has low mechanical strength at high temperatures.
Accordingly, a variety of attempts have been made with the aim of developing a heat resistant material improved in the above-mentioned respects by the use of base materials hitherto employed. Among these heat resistant materials, polyaminobismaleimide resin (U.S. Pat. No. 3,562,223) is noteworthy because of its very small linear expansion coefficient, its excellent mechanical properties at high temperatures and its long heat life. Apart from it, there have been proposed a combination of N,N'-substituted bis-maleimide and a polyamine having maleimide ring obtainable by reacting maleic anhydride with an aromatic diamine (Japanese Pat. Application Kokoku (Post-Exam Publication) No. 16156/1977), a combination of an epoxy compound and a polyaminobismaleimide obtainable by adding a diamine to N,N'-substituted bismaleimide (Japanese Pat. Application Kokoku (Post-Exam Publication) No. 5920/1978) and the like.
However, the above-mentioned polyaminobismaleimide resins still have a fault in that the reaction product between maleic anhydride and a diamine or the N,N'-substituted bis-maleimide compound, i.e. the starting material, is expensive because its synthesis necessitates a large quantity of polar solvent and if such a polar solvent is not used, the reaction cannot proceed uniformly so that the resin composition obtained therefrom is poor in moldability and its cured product is inferior in properties.